The present invention relates to a method of assembly of a string of drilling elements, such as, for example, drill pipes, in which at least one obstruction element is inserted as a safety device, for drilling wells for oil-field exploration and development in deep and ultra-deep waters, such as seas or watersheds. The present invention further relates to an obstruction element acting as a safety device and to the use thereof in said string of said drilling elements.
The obstruction element acting as a safety device, which is inserted in the drill string according to the present invention, protects the environment and the life of the crew of a drilling rig, because it prevents an uncontrolled outflow of layer fluids, also known as blowout, through the inside of the drilling elements, e.g. drill pipes.
The obstruction element acting as a safety device according to the present invention operates automatically and ensures that the pipes will be closed internally. Moreover, during the well drilling cycle said obstruction element is positioned under the blowout preventer (BOP), thus ensuring that the shear rams comprised in BOP will be able to cut the pipe properly and sharply, since the drilling element or pipe will not be concerned by an anomalous internal pressure that might adversely affect the cutting.
For the purposes of the present invention, the term deepwater drilling relates to a drilling process carried out into the bed of a sea, an ocean or a watershed in general, the depth of said bed being at least 550 m, whereas ultra-deepwater drilling refers to a depth of at least 1500 m from the water level.
It is known that in deepwater drilling, in particular in very deep waters, the actual drilling of the bottom or bed occurs after a string of drilling elements or pipes has already been assembled, the length of which equals the depth of the bottom or bed. Other drilling elements are then added to this first string of elements to allow the drilling rig to execute the drilling cycle, as known to the man skilled in the art.
By way of example, in order to drill 1500 m with a water depth of 1000 m from sea level, it will be necessary to assemble a 2500 m pipe string.
It is also known that, in deepwater drilling, the blowout preventer (BOP) for preventing an undesired outflow of hydrocarbons from a drilling well, is positioned on the bottom or bed, i.e. very distant from the drill floor where the drilling elements are assembled to form the string.
In the drilling field, all those who design and drill wells rely on the concept that at least two independent and tested safety barriers must be available. In most cases, the two safety barriers respectively consist of: the circulating drilling mud, the gradient of which is higher than the gradient of the pores of the formation being crossed; and the safety equipment installed and tested at the wellhead.
For the purposes of the present invention, the term wellhead relates to the point where the drilling well begins, which in deepwater drilling is on the bottom or bed of the watershed.
In the technical jargon used in the oil well drilling industry, the safety equipment essentially consists of the blowout preventer (BOP).
Current BOP's can hold operating pressures in the range of 3,000 to 15,000 psi, i.e. 20.68 MPa to 103.4 MPa, in deepwater drilling. For ultra-deepwater drilling, BOP's are typically used which work at pressures in the range of 10,000 to 15,000 psi, i.e. 68 MPa to 103.4 MPa. BOP's include a set of clamping devices, such as rams, to clamp the drilling elements, and a plurality of shearing elements to shear the drilling elements. In particular, a BOP for deepwater use comprises at least three profiled rams, one blind ram, and one or two shear rams, which close the wellhead. Said BOP also comprises closing elements called annulars, which can exert a pressure in the range of 5,000 to 10,000 psi, i.e. approx. 34.47 MPa to 68.93 MPa. Normally the device includes one upper closing element, or upper annular, and one lower closing element, or lower annular.
Said closing elements can close any drilling element or drill pipe of any common size, and can even exert a blind closing action by closing the through hole comprised in said drilling element, as is known to a man skilled in the art.
In the prior art, shear rams have been introduced for offshore activities on semi-submersible craft and drill ships, for the purpose of being able to shear the pipes in dangerous situations and move away with the drilling craft, leaving at the bottom of the sea a well closed at its head by safety equipment.
Said hydrocarbon blowout preventer or BOP normally comprises an upper portion and a lower portion. Said upper portion is separable from the lower portion, which will remain on the bottom or bed, integral with the wellhead. This separation of the BOP into two portions allows safeguarding the life of the crew aboard the floating craft or structure normally employed for deepwater drilling, while at the same time ensuring a safe closing of the well.
Said removed upper portion of the BOP can be reconnected to the safety system left at the wellhead, and drilling activities can then be resumed.
The cutting of the well pipes effected by the shear rams of the BOP is considered to be the last action that should be taken because, by so doing, hydraulic contact with the well will be lost and all actions aiming at restoring the normal safety and working conditions at the well will then be precluded. It follows that, if this extreme action is the only option that is left, the BOP will need to be in the best conditions for performing the cutting.
It is known that the BOP ensures the best cutting results on drilling elements or drill pipes in the well when inside said pipes there is the nominal working pressure, i.e. no anomalous pressure.
For the purposes of the present invention, the term anomalous pressure refers to a pressure higher than the pressure which is present inside the drilling elements during the drilling cycle. In particular, an anomalous pressure is a pressure higher than the maximum drilling mud intake pressure.
Said anomalous pressure normally causes an uncontrolled outflow of hydrocarbons, or blowout. In particular, if blowout occurs through the inside of the drill pipes, the BOP device will not operate in optimal working conditions. It can therefore be presumed that the shear rams will not be able to cut the pipe with anomalous internal pressure and to properly seal the well. Moreover, depending on the reservoir pressures, the value of the pressure inside the drill pipes may vary considerably.
The actual trend is to build increasingly powerful and robust prevention systems or BOP's, even including two shearing parts, without however paying attention to the above-mentioned concept, according to which it must be ensured that, during the step of shearing the drilling elements, the pressure conditions inside the pipes must be such as to allow the shear rams to work in the best operating conditions.
Therefore, notwithstanding the high power of these new prevention devices or BOP's, problems might be easily encountered while cutting pipes in high-pressure and high-temperature well conditions, also known as HP/HT.
It is also known to use a valve assembly in series with the through hole of the drilling element of a drill string, aiming at preventing the drilling mud, during continuous mud circulation, from flowing out on the drill floor while adding or removing one or more drilling elements to/from said string, as described, for example, in U.S. Pat. No. 3,298,385.
It is known from US patent application US2013/175045 A1 a method for pressurizing a hydraulic accumulator includes creating an annulus pressure zone in hydraulic communication with the hydraulic accumulator through a hydraulic recharging circuit and applying a hydraulic pressure to the annulus pressure zone. Operating the hydraulic recharging circuit in response to applying the hydraulic pressure and pressurizing the hydraulic accumulator in response to operating the hydraulic recharging circuit.
It is also known from US patent application US2005/284547 A1 components of a subsurface safety valve which are cast instead of machined for dramatic cost savings. In particular, the flapper is cast from a 718 nickel alloy and treated with the HIP process to increase strength and corrosion resistance while reducing porosity. Other downhole valve components are contemplated to be produced by the same technique and the materials can also be varied. Depending on the specific alloys, the resulting HIP components are either superior in performance (e.g. strength, corrosion resistance) or considerably cheaper to manufacture than their wrought counterparts.
The European patent application EP0697501 discloses Integrated drilling and evaluation system for drilling, logging and testing a well comprises a drill string (18A), a drill bit (30) carried on a lower end of the drill string for drilling a well bore, logging while drilling means (28) included in the drill string for identifying subsurface zones of formations (16) of interest, packer means (24) carried on the drill string above the drill bit (30) for sealing a zone or formation (16) of interest below the packer means (24), and a fluid testing means (22) included in the drill string for controlling the flow of well fluid from the zone or formation of interest into the drill string. The system allows one or more subsurface zones or formations (16) of interest in a well to be drilled, logged and tested without the necessity of removing the drill string (18A) from the well.
At last, the U.S. Pat. No. 6,196,261 discloses a flapper valve assembly (120) for controlling fluid flow therethrough is disclosed. The flapper valve assembly (120) comprises a tubular valve housing having a valve chamber. A valve seat (124) is mounted within the housing. The valve seat (124) has a valve seat sealing surface (126). The valve seat (124) also has an internal load bearing shoulder (134). A flapper closure plate (122) is rotatably disposed within the valve chamber. The flapper closure plate (122) is rotatable between a valve open position in which the flapper closure plate (122) is removed from the valve seat (124) and a valve closed position in which the sealing surface (128) of the flapper closure plate (122) sealingly engages the valve seat sealing surface (126) for preventing flow through the flapper valve assembly (120). The maximum travel of the flapper closure plate (122) in the closed position is defined by the internal load bearing shoulder (134) of the valve seat (124).